Some aircraft are equipped with VHF Omni Ranging (VOR) radio receivers for enroute navigation and with Instrument Landing System (ILS) and Global Navigation Satellite System (GNSS) Landing System (GLS) receivers for precision approach navigation used during aircraft landing. ILS receivers include a Localizer VHF radio receiver to receive horizontal guidance signals for the selected airport runway. GLS receivers include a VHF data broadcast (VDB) receiver to receive the GLS glide path way points and the local Differential GNSS (DGNSS) corrections applicable to the runway selected for landing.
Because simultaneous reception of VOR and ILS Localizer or GLS VDB signals is required during initial approach and during aborted auto-land operations, many aircraft are equipped with two VHF receivers for VOR and two VHF receivers for either ILS Localizer or GLS VDB reception. Thus, many aircraft have four or more VHF receivers. A means to reduce the number of VHF receivers that must be fed by the VOR antenna is desired.